Yeah, yeah, the Appalachian Mountains are old. We’re told all the time: The Appalachian Mountains are old.
Most of the time, this is used as an excuse. “Hey East Coast, why are your mountains so charming and rolling and welcoming instead of sheer and jagged and mighty? Why do they make me feel nostalgic and comforted instead of feeling like I just saw the face of God and lived?” Uhh…uhh…uhh…They’re old!
Loser mountains.
It’s not only an excuse, though, it turns out. It turns out the Appalachian Mountains really are quite old. Old enough that it’s super cool how old they are.
The Appalachian Mountains are only one part of a legendary team of mountains which once ruled the non-ocean world. We were tipped off on this by a promoted Facebook post, and that post wasn’t all that accurate, but it had the right idea. The Appalachian Mountains got ripped apart from its friends by continental drift. They and those friends used to cover an even bigger area, and their long-lost relatives live overseas.
Trying to learn about this from Wikipedia and assorted other sources (the National Park Service, Science Magazine, Brown University, looking for certified geologists on Quora) is overwhelming, so we’re going to start this with a little timeline I think is close enough to correct to be useful:
- ~500M Years Ago: Appalachian Mountains start forming (volcanic activity on the coast of one of the continents which formed Pangea).
- ~350M Years Ago: Pangea forms, the Appalachian Mountains get a lot bigger (thanks to the collision which forms Pangea).
- ~175M Years Ago: Pangea begins to break apart.
- 1971: John Denver releases Poems, Prayers & Promises.
That’s my impression of all of this. The Appalachian Mountains were built over a long period of time, they started construction way before Pangea existed, but Pangea’s existence is what made them so incredibly tall before Pangea broke up and erosion did its thing.
Here are the details.
From what I’m gathering, the Appalachian Mountains first started to form almost 500 million years ago during volcanic activity on the coast of Laurentia, a continent which would go on to become most of North America today. The coast of Laurentia stretched on our modern map from eastern Greenland down through the Canadian Maritimes all the way to the Texas Hill Country (and then back up again, but we’ll get to that), but only part of that coast became the Appalachians. Another part became the Ouachita Mountains, over in Arkansas and Oklahoma. Other parts didn’t become mountains at all. The hills in the Texas Hill Country became hills because of erosion, not because of any mountain-building activity. If you keep going around the Laurentian coast, wrapping north from modern-day El Paso, you’re going through the modern-day western U.S. and Canada, but all the mountains over there didn’t form until Laurentia had long since been welded together into the broader North American Plate. At least, that’s what I’m seeing from Wikipedia and assorted other sources. Here’s a map, from Laurentia’s Wikipedia page, where they’re calling Laurentia the North American Craton.
Eventually, Laurentia crashed into the continents of Avalonia and Baltica to form Laurasia, and then Gondwana crashed into that. That was the dramatic one. That was what formed Pangea. From what I can tell, there was a Y-shaped collection of mountain ranges stretching across the various continental borders that were crashing into each other. The vertex of the Y was between modern-day Greenland, Scotland, and Scandinavia. The foot of the Y stretched down the Laurentian coast (that’s the Appalachians and the Ouachitas), but also down part of modern-day Africa’s northwest coast (the Little Atlas Mountains in Morocco were part of these, but the broader Atlas Mountains didn’t exist yet). That seam got ripped apart when the Atlantic opened. The left branch of the Y stretched up Greenland and Scandinavia, while the right branch went over into what’s now Germany and Poland, along the border of what was the continent of Baltica. Here’s one depiction of that Y, from the Wikipedia page for the Caledonian Orogeny. This was before Gondwana showed up.
The right branch of this Y was bigger than the left branch, presumably because the right branch formed from a bigger collision—that of Gondwana into Laurasia rather than Laurentia and Avalonia into Baltica. The foot of the Y and the right branch, then, formed the Central Pangean Mountains, which were gigantic. These are the ones which get compared to the Himalayas today. My impression is that although the Appalachians were already there, this is when they really blew up, getting physically pushed upwards before eventually getting pulled away from their friends and then eroded down into their folk music-inducing present shape. Here’s a map from the Wikipedia page for the Central Pangean Mountains.
The Central Pangean Mountains are the legendary ones. They included the Appalachians, the Ouachitas, the Scottish Highlands, the Little Atlas Mountains, and maybe even more. Now, they’re mostly little, because they are very, very old, and mountains get smaller (from erosion) once they stop getting bigger (from all the things which build mountains). The Appalachians were one part of them. The parts had different origins, but they were all involved in the collision between Gondwana and Laurasia. That was what made them so big and therefore legendary.
I think this last part is important—that the mountain ranges kind of existed but then had a joint event which linked them together. I don’t know if you think regularly about continental drift, or if that’s just me, and if you do think about it I don’t know if we think about it in the same way. The way I think about it, though, is as a bunch of little pieces of land floating around bumping into each other and then breaking apart. When they collide, they make mountains, when they separate, they make oceans. At a simple level, this does seem correct, but the thing I struggle to grasp is how long this has been happening and how much is happening and how things layer on top of one another over time. Plate tectonics is neat and tidy when you look back from our current global shape to that of Pangea, and then a little further back to Laurasia and Gondwana. But even around those major movements, there are all these little actions on the edges making their own little mountain ranges and their own coastal plains and their own plateaus, and then those get involved in other little actions or in big bad collisions and the shape changes even more, but in varied ways. Beyond that, you’ve got everything that preceded Laurasia and Gondwana, giving places within those masses their own unique shapes and features which predate those continents forming (in other words, they predate the continents which predate the continent which predates our continents). Then, you’ve got other things (mostly erosion) shaping terrain from the top, creating hills and lakes and straits and rivers and the island of Manhattan, upon which humans built things capable of at least affecting the weather. Plate tectonics is neat and tidy when you look at a map and see how neatly Brazil should tuck into Africa. If you start digging deeper, it gets really messy, fast. We also don’t know all that much about it yet. We know a lot, but we don’t know everything, like why Missouri can get earthquakes capable of shaking most of the population of the United States.
So, the Appalachians are older than Pangea. Kind of. But Pangea is what gave them their street cred.
